Laser rangefinders, which measure distances by detecting the phase shift of intensity modulated laser light reflected by objects, are very useful for obtaining 3-D models of the surrounding environment. A drawback of single-frequency laser rangefinders is that the phase measurement is always ambiguous. The consequence of this phase ambiguity is a range ambiguity interval equal to one-half of the wavelength of the modulation signal. Objects outside this interval are not ranged correctly. This thesis describes the theory and implementation of a dual-frequency laser rangefinding system in which the sum of two sinusoidal signals modulates the laser intensity. The resulting two ambiguous distance measurements are used to calculate the true distance to the target. This method allows a greater ambiguity interval without sacrificing measurement accuracy. The system built at Rice University has performed as expected, verified the algorithms and theories presented, and demonstrated the practicality of dual-frequency laser rangefinders.